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  • Python - what's your conventions to declare your attributes in a class ?

    - by SeyZ
    Hello, In Python, I can declare attributes all over the class. For example : class Foo: def __init__(self): self.a = 0 def foo(self): self.b = 0 It's difficult to retrieve all attributes in my class when I have a big class with a lot of attributes. Is it better to have the following code (a) or the next following code (b) : a) Here, it's difficult to locate all attributes : class Foo: def __init__(self): foo_1() foo_2() def foo_1(self): self.a = 0 self.b = 0 def foo_2(self): self.c = 0 b) Here, it's easy to locate all attributes but is it beautiful ? class Foo: def __init__(self): (self.a, self.b) = foo_1() self.c = foo_2() def foo_1(self): a = 0 b = 0 return (a, b) def foo_2(self): c = 0 return c In a nutshell, what is your conventions to declare your attributes in a class ?

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  • Python: How To copy function parameters into object's fields effortlessly ?

    - by bandana
    Many times I have member functions that copy parameters into object's fields. For Example: class NouveauRiches(object): def __init__(self, car, mansion, jet, bling): self.car = car self.mansion = mansion self.jet = jet self.bling = bling Is there a python language construct that would make the above code less tedious? One could use *args: def __init__(self, *args): self.car, self.mansion, self.jet, self.bling = args +: less tedious -: function signature not revealing enough. need to dive into function code to know how to use function -: does not raise a TypeError on call with wrong # of parameters (but does raise a ValueError) Any other ideas? (Whatever your suggestion, make sure the code calling the function does stays simple)

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  • Why doesn't Python's `re.split()` split on zero-length matches?

    - by Tim Pietzcker
    One particular quirk of the (otherwise quite powerful) re module in Python is that re.split() will never split a string on a zero-length match, for example if I want to split a string along word boundaries: >>> re.split(r"\s+|\b", "Split along words, preserve punctuation!") ['Split', 'along', 'words,', 'preserve', 'punctuation!'] instead of ['', 'Split', 'along', 'words', ',', 'preserve', 'punctuation', '!'] Why does it have this limitation? Is it by design? Do other regex flavors behave like this?

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  • How do I change my current directory from a python script?

    - by misterloogs
    I'm trying to implement my own version of the 'cd' command that presents the user with a list of hard-coded directories to choose from, and the user has to enter a number corresponding to an entry in the list. The program, named my_cd.py for now, should then effectively 'cd' the user to the chosen directory. Example of how this should work: /some/directory $ my_cd.py 1) ~ 2) /bin/ 3) /usr Enter menu selection, or q to quit: 2 /bin $ Currently, I'm trying to 'cd' using os.chdir('dir'). However, this doesn't work, probably because my_cd.py is kicked off in its own child process. I tried wrapping the call to my_cd.py in a sourced bash script named my_cd.sh: #! /bin/bash function my_cd() { /path/to/my_cd.py } /some/directory $ . my_cd.sh $ my_cd ... shows list of dirs, but doesn't 'cd' in the interactive shell Any ideas on how I can get this to work? Is it possible to change my interactive shell's current directory from a python script?

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  • Whats the python way for recursively setting file permissions?

    - by Geoff
    What's the "python way" to recursively set the owner and group to files in a directory? I could just pass a 'chown -R' command to shell, but I feel like I'm missing something obvious. I'm mucking about with this: import os path = "/tmp/foo" for root, dirs, files in os.walk(path): for momo in dirs: os.chown(momo, 502, 20) This seems to work for setting the directory, but fails when applied to files. I suspect the files are not getting the whole path, so chown fails since it can't find the files. The error is: 'OSError: [Errno 2] No such file or directory: 'foo.html' What am I overlooking here?

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  • Is it inefficient to access a python class member container in a loop statement?

    - by Dave
    Hi there. I'm trying to adopt some best practices to keep my python code efficient. I've heard that accessing a member variable inside of a loop can incur a dictionary lookup for every iteration of the loop, so I cache these in local variables to use inside the loop. My question is about the loop statement itself... if I have the following class: class A(object): def init(self) self.myList = [ 'a','b','c', 'd', 'e' ] Does the following code in a member function incur one, or one-per-loop-iteration (5) dictionary lookups? for letter in self.myList: print letter IE, should I adopt the following pattern, if I am concerned about efficiency... localList = self.myList for letter in localList: print letter or is that actually LESS efficient due to the local variable assign? Note, I am aware that early optimization is a dangerous pitfall if I'm concerned about the overall efficiency of code development. Here I am specifically asking about the efficiency of the code, not the coding. Thanks in advance! D

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  • Do Managers in Python Multiprocessing module lock the shared data?

    - by AnonProcess
    This Question has been asked before: http://stackoverflow.com/questions/2936626/how-to-share-a-dictionary-between-multiple-processes-in-python-without-locking However I have several doubts regarding the program given in the answer: The issue is that the following step isn't atomic d['blah'] += 1 Even with locking the answer provided in that question would lead to random results. Since Process 1 read value of d['blah'] saves it on the stack increments it and again writes it. In Between a Process 2 can read the d['blah'] as well. Locking means that while d['blah'] is being written or read no other process can access it. Can someone clarify my doubts?

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  • Python subprocess.Popen hangs in 'for l in p.stdout' until p terminates, why?

    - by Albert
    I have that code: #!/usr/bin/python -u localport = 9876 import sys, re, os from subprocess import * tun = Popen(["./newtunnel", "22", str(localport)], stdout=PIPE, stderr=STDOUT) print "** Started tunnel, waiting to be ready ..." for l in tun.stdout: sys.stdout.write(l) if re.search("Waiting for connection", l): print "** Ready for SSH !" break The "./newtunnel" will not exit, it will constantly output more and more data to stdout. However, that code will not give any output and just keeps waiting in the tun.stdout. When I kill the newtunnel process externally, it flushes all the data to tun.stdout. So it seems that I can't get any data from the tun.stdout while it is still running. Why is that? How can I get the information? Note that the default bufsize for Popen is 0 (unbuffered). I can also specify bufsize=0 but that doesn't change anything.

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  • Python: How can I override one module in a package with a modified version that lives outside the pa

    - by zlovelady
    I would like to update one module in a python package with my own version of the module, with the following conditions: I want my updated module to live outside of the original package (either because I don't have access to the package source, or because I want to keep my local modifications in a separate repo, etc). I want import statements that refer to original package/module to resolve to my local module Here's an example of what I'd like to do using specifics from django, because that's where this problem has arisen for me: Say this is my project structure django/ ... the original, unadulterated django package ... local_django/ conf/ settings.py myproject/ __init__.py myapp/ myfile.py And then in myfile.py # These imports should fetch modules from the original django package from django import models from django.core.urlresolvers import reverse # I would like this following import statement to grab a custom version of settings # that I define in local_django/conf/settings.py from django.conf import settings def foo(): return settings.some_setting Can I do some magic with the __import__ statement in myproject/__init__.py to accomplish this? Is there a more "pythonic" way to achieve this?

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  • How do I delete a curse window in python and restore background window?

    - by Zloy Smiertniy
    Hell-o guys, I'm working on python curses and I have my initial window with initscr() and I create several new windows to overlap it, I want to know if I can delete these windows and restore the standard screen without having to refill it. Is there a way? I can also ask if someone can tell me the difference between a window, subwindow, pad and sub pad. I have this code: stdscr = curses.initscr() Then I fill it with random letters stdscr.refresh() newwin=curses.newwin(10,20,5,5) newwin.touchwin() newwin.refresh() I want to delete newwin here so that if I write stdscr.refresh() newwin won't appear stdscr.touchwin() stdscr.refresh() And here it should appear as if no window was created.

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  • Rounding issue when adding floats in python, is this normal?

    - by thepearson
    I just wanted to know if this behavior is expected. If so, can someone explain to me why. This has probably been answered elsewhere I can't seem to find it using Google. Probably not searching with the right terms. I am running Ubuntu 10.04. Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> var = 10.0 >>> var 10.0 >>> var + 5 15.0 >>> var + 5.1 15.1 >>> var + 5.2 15.199999999999999 >>>

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  • How should I build a simple database package for my python application?

    - by Carson Myers
    I'm building a database library for my application using sqlite3 as the base. I want to structure it like so: db/ __init__.py users.py blah.py etc.py So I would do this in Python: import db db.users.create('username', 'password') I'm suffering analysis paralysis (oh no!) about how to handle the database connection. I don't really want to use classes in these modules, it doesn't really seem appropriate to be able to create a bunch of "users" objects that can all manipulate the same database in the same ways -- so inheriting a connection is a no-go. Should I have one global connection to the database that all the modules use, and then put this in each module: #users.py from db_stuff import connection Or should I create a new connection for each module and keep that alive? Or should I create a new connection for every transaction? How are these database connections supposed to be used? The same goes for cursor objects: Do I create a new cursor for each transaction? Create just one for each database connection?

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  • Is there a difference between `==` and `is` in python?

    - by Bernard
    My Google-fu has failed me. In Python, are these: n = 5 # Test one. if n == 5: print 'Yay!' # Test two. if n is 5: print 'Yay!' two tests for equality equivalent (ha!)? Does this hold true for objects where you would be comparing instances (a list say)? Okay, so this kind of answers my question: l = list() l.append(1) if l == [1]: print 'Yay!' # Holds true, but... if l is [1]: print 'Yay!' # Doesn't. So == tests value where is tests to see if they are the same object?

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  • How do I build a python string from a raw (binary) ctype buffer?

    - by fcrazy
    I'm playing with Python and ctypes and I can't figure out how to resolve this problem. I call to a C function which fills a raw binary data. My code looks like this: class Client(): def __init__(self): self.__BUFSIZE = 1024*1024 self.__buf = ctypes.create_string_buffer(self.__BUFSIZE) self.client = ctypes.cdll.LoadLibrary(r"I:\bin\client.dll") def do_something(self): len_written = self.client.fill_raw_buffer(self.__buf, self.__BUFSIZE) my_string = repr(self.__buf.value) print my_string The problem is that I'm receiving binary data (with 0x00) and it's truncated when I tried to build my_string. How can I build my_string if self._buf contains null bytes 0x00? Any idea is welcome. Thanks

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  • How to input test data using the DecisionTree module in python?

    - by lifera1n
    On the Python DescisionTree module homepage (DecisionTree-1.6.1), they give a piece of example code. Here it is: dt = DecisionTree( training_datafile = "training.dat", debug1 = 1 ) dt.get_training_data() dt.show_training_data() root_node = dt.construct_decision_tree_classifier() root_node.display_decision_tree(" ") test_sample = ['exercising=>never', 'smoking=>heavy', 'fatIntake=>heavy', 'videoAddiction=>heavy'] classification = dt.classify(root_node, test_sample) print "Classification: ", classification My question is: How can I specify sample data (test_sample here) from variables? On the project homepage, it says: "You classify new data by first constructing a new data vector:" I have searched around but have been unable to find out what a data vector is or the answer to my question. Any help would be appreciated!

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  • how could it works if function is called before it is defined in python?

    - by user2131316
    I was wondering what does if __name__ == "__main__": really do in python, I have the following code in python3: def main(): test(); def test(): print("hello world " + __name__); if __name__ == "__main__": main(); we know that we have to declare a function before we use it, so function call inside of if part works fine, the main() is defined before it is called inside of if statement, but what about the test() function, it is defined after it is called and there is no errors: def main(): test(); def test(): print("hello world " + __name__); so how could it works if the test() function is defined after it is called?

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  • How to enter decimal/binary numbers when creating byte objects in python?

    - by Eric
    I'm using python 3.1.1. I know that I can create byte objects using the byte literal in the form of b'...'. In these byte objects, each byte can be represented as a character(in ascii code if I'm not wrong) or as a hexadecimal/octal number. Hexadecimal and octal numbers can be entered using an escape of \x for hexadecimal numbers and just a \ for octal numbers. However, there's no escape sequences for decimal or binary numbers. Is there any way to enter them into byte objects?

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  • How can I write to the previous line in a log file using Python's Logging module?

    - by turvyc
    Hi all, long-time lurker here, finally emerging from the woodwork. Essentially, what I'm trying to do is have my logger write data like this to the logfile: Connecting to database . . . Done. I'd like the 'Connecting to database . . . ' to be written when the function is called, and the 'Done' written after the function has successfully executed. I'm using Python 2.6 and the logging module. Also, I'd really like to avoid using decorators for this. Any help would be most appreciated!

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  • Online compilers/runtime for Java, C++, Python and ObjC?

    - by Nocturne
    Does anyone know of a good online compiler/runtime (for C++, Java, Python, ObjC etc.) that I can access on the web? What I'm looking for is something that would allow me to type in a program in a web form and to run the program and see the results online. (Let's not get into the why for now. Suffice it to say for the moment that I don't always have access to a compiler/runtime, and firing up an IDE is just overkill for testing out some code snippets) I know of codepad.org -- but I'm looking for something better.

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  • Good real-world uses of metaclasses (e.g. in Python)

    - by Carles Barrobés
    I'm learning about metaclasses in Python. I think it is a very powerful technique, and I'm looking for good uses for them. I'd like some feedback of good useful real-world examples of using metaclasses. I'm not looking for example code on how to write a metaclass (there are plenty examples of useless metaclasses out there), but real examples where you have applied the technique and it was really the appropriate solution. The rule is: no theoretical possibilities, but metaclasses at work in a real application. I'll start with the one example I know: Django models, for declarative programming, where the base class Model uses a metaclass to fill the model objects of useful ORM functionality from the attribute definitions. Looking forward to your contributions.

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  • How do I use python wx:Config to access the Windows registry?

    - by GreenAsJade
    I've read http://wxpython.org/docs/api/wx.ConfigBase-class.html I've done some basic things like the appended. What I can see is that Config.Create() returns me some sort of configuration object, which has information about python in it. But clearly that's not what I'm looking for: I seem to be missing the magic to say "give me a Config that is the Windows Registry"... Thanks! GaJ import wx from wx import Config app=wx.App(False) config=Config.Create() config.HasGroup("HKEY_CURRENT_USER") False config.GetFirstEntry() (0, u'', -1) config.GetFirstGroup() (1, u'PythonCore', 1) config.GetNextGroup(1) (0, u'', -1) config.GetNumberOfGroups() 1 config.GetPath() u'' config.HasEntry("PythonCore") False config.GetFirstGroup() (1, u'PythonCore', 1)

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  • Changing floating point behavior in Python to Numpy style.

    - by Tristan
    Is there a way to make Python floating point numbers follow numpy's rules regarding +/- Inf and NaN? For instance, making 1.0/0.0 = Inf. >>> from numpy import * >>> ones(1)/0 array([ Inf]) >>> 1.0/0.0 Traceback (most recent call last): File "<stdin>", line 1, in <module> ZeroDivisionError: float division Numpy's divide function divide(1.0,0.0)=Inf however it is not clear if it can be used similar to from __future__ import division.

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  • How to delete files with a Python script from a FTP server which are older than 7 days?

    - by Tom
    Hello I would like to write a Python script which allows me to delete files from a FTP Server after they have reached a certain age. I prepared the scipt below but it throws the error message: WindowsError: [Error 3] The system cannot find the path specified: '/test123/*.*' Do someone have an idea how to resolve this issue? Thank you in advance! import os, time from ftplib import FTP ftp = FTP('127.0.0.1') print "Automated FTP Maintainance" print 'Logging in.' ftp.login('admin', 'admin') # This is the directory that we want to go to directory = 'test123' print 'Changing to:' + directory ftp.cwd(directory) files = ftp.retrlines('LIST') print 'List of Files:' + files # ftp.remove('LIST') #------------------------------------------- now = time.time() for f in os.listdir(directory): if os.stat(f).st_mtime < now - 7 * 86400: if os.directory.isfile(f): os.remove(os.directory.join(directory, f)) #except: #exit ("Cannot delete files") #------------------------------------------- print 'Closing FTP connection' ftp.close()

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  • What is a good cms that is postgres compatible, open source and either php or python based?

    - by hackg
    Php or python Use and connect to our existing postgres databases open source / or very low license fees Common features of cms, with admin tools to help manage / moderate community have a large member base on very basic site where members provide us contact info and info about their professional characteristics. About to expand to build new community site (to migrate our member base to) where the users will be able to msg each other, post to forums, blog, share private group discussions, and members will be sent inivitations to earn compensation for their expertise. Profile pages, job postings, and video chat would be plus. Already have a team of admins savvy with web apps to help manage it but our developer resources are limited (3-4 programmers) and looking to save time in development as opposed to building our new site from scratch.

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  • Correct way to protect a private API key when versioning a python application on a public git repo

    - by systempuntoout
    I would like to open-source a python project on Github but it contains an API key that should not be distributed. I guess there's something better than removing the key each time a "push" is committed to the repo. Imagine a simplified foomodule.py : import urllib2 API_KEY = 'XXXXXXXXX' urllib2.urlopen("http://example.com/foo?id=123%s" % API_KEY ).read() What i'm thinking is: Move the API_KEY in a second key.py module importing it on foomodule.py; i would then add key.py on .gitignore file. Same as 1 but using ConfigParser Do you know a good programmatic way to handle this scenario?

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